High voltage bushing



Nov. 4, 1958 D. L: JOHNSTON ETAL HIGH VOLTAGE BUSHING Filed Jan. 25, 1955 L 2 J M 3 u a y w 3 F n 2 4 iiiiiiiiiu :M L H W 5 4 5 A H l m; 0 0 v d Z :1 I II NIH} I .w. m 6 7m II Q 2 Z a I,

United States Patent HIGH VOLTAGE BUSHING Donald L. Johnston and William A. Wooldridge, Pittsfield, Mass., assignors to General Electric Company, a corporation of New York Application January 25, 1955, Serial No. 483,977 9 Claims. (Cl. 174-12) This invention relates to bushings, and more in particular to an improved upper terminal assembly for a high voltage insulating bushing for electrical apparatus.

High voltage bushings are generally comprised of a central conducting axial tube surrounded by a plurality of cylinders of insulating material, with the entire assembly being surrounded by ceramic shells. The ceramic shells form the external radial surface of the bushing. An electrical terminal is provided at the top end of the bushing, and this terminal may be connected to the central axial tube or to a cable passing through the tube.

Such bushings may be held together by means of clamping plates over both ends of the assembly. Locking nuts threaded to the central conductor provide a compressive force for the clamping plates. A metallic flange extending radially from between the ceramic shells provides means for mounting the bushings.

In order that such a bushing may be filled with a dielectric fluid such as oil for improving the insulation characteristics thereof, suitable gaskets are provided between the component parts. An enclosed chamber is provided at the top of the bushing to enable the oil to expand without damaging the assembly. In order that the bushing is not damaged due to difference in expansion coeflicients of the central conductor and the ceramic shell, various resilient assemblies may be employed, the more common method being to locate the assemblies between the top locking nut and the top clamping plate. This allows the ceramic shells and the central conductor to expand or contract independently of each other.

The bushings described above may be used with various modifications on many types of equipment, such as, for example, on high voltage transformers, and circuit breakers. For transformer use, the bushing is provided with a conducting cable extending through the central axial tube between the top terminal and the transformer windings. Since it is desirable that the transformer oil does not mix with and contaminate the bushing oil, flexible seal means are provided between the top of the central axial tube and the top terminal. The conducting cable extends axially through the flexible seal. When the bushing is used on a circuit breaker, no central cable is required, and the current is carried by the central axial tube. In the latter case the tube is usually sealed at the bottom with a cap nut. In this case flexible conductors connect the top of the central axial tube to the top terminal.

In the past, bushings for transformers and circuit breakers were not interchangeable, each type having its own special design. Thus, although the two types of bushing were similar in many respects, significant differences necessitated either stocking of both types in the event of breakdown, or removing a piece of equipment from service until a replacement could be obtained. Due to the high cost of the larger bushings, it was not always economically feasible to have an extra bushing of each type on hand in case of emergency. From the manufacturers standpoint, it was necessary to stock both types of bushings, as well as the separate parts for both types.

It is therefore an object of this invention to provide a high voltage bushing that may be used for both circuit breakers and power transformers.

A further object of this invention is to provide an im proved high voltage bushing having flexible seal means for preventing contamination of the bushing oil when used on a power transformer, and flexible conducting means adapted to carry-the current when the bushing is used on a circuit breaker.

Briefly stated, in one embodiment of this invention we provide a high voltage bushing having a hollow central axial conductor. The upper end of the conductor is connected to the top terminal by means of a metallic bellows, the bellows providing a flexible seal to prevent oil leakage between the bushing expansion chamber and the central conductor. A plurality of flexible braid conductors are connected bridging the bellows, and provide a path for current when no central cable is used.

This invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a cross sectional view of one embodiment of the high voltage bushing of this invention; Fig. 2 is a cross-sectional view of the top terminal and ex pansion chamber assembly of Fig. 1 as it appears when the bushing is used on a circuit breaker, and Fig. 3 is a cross sectional view of the top terminal and expansion chamber assembly of Fig. l as it appears when the bushing is used on a power transformer.

Referring now to the drawing, and more in particular to Fig. 1, therein is illustrated a bushing comprised of a hollow central axial conductor 11 having threaded ends. The central conductor is surrounded by a plurality of cylinders 12 of insulating material in accordance with the usual practice in the construction of high voltage bushings. A lower ceramic shell 13, a metal cylinder 14, and an upper ceramic shell 15 form an outer covering for the conductor assembly, and are held in compression by means of a lower clamping plate 16 threaded to the lower end of the central conductor 11 and an upper clamping plate 17 fitted over the upper end of the central conductor 11. The upper clamping plate 17 is resiliently held in place by means of a spring assembly in order to allow for different coeflicients of expansion of the outer shells and the central conductor. The spring assembly as illustrated consists of a coil spring 18 held in compression between two seated washers 19 and 20 by the action of a locking nut 21 (see Fig. 2). Other types of spring assemblies may also be utilized for this purpose withoutdeparting from the scope of this invention.

Referring again to Fig. 1, an expansion chamber 22 is mounted on top of the upper clamping plate, and a top terminal assembly 23 is mounted on the top wall of the expansion chamber. The top terminal assembly is comprised of a cover plate 24 which is mounted over a central hole in the top wall of the expansion chamber, and a top terminal 25 which is mounted on top of the cover plate 24. The connection between the top end of the central conductor 11 and the top terminal assembly 23 may be more clearly seen in Figs. 2 and 3, wherein it is shown that flanged metallic tube 26 having its flanges compressed between the top of the expansion chamber 22 and the cover plate 24 and has a metallic bellows 27 sealed to its lower end. A straight tube section 28 is sealed to the bottom end of bellows 27, and is also sealed to a nut 29 threaded onto the upper end of the central conductor 11. A plurality of conducting braids 30 bridge the bellows and are connected to tubes 26 and 28 by means of clips 31 brazed to the tubes.

The entire bushing is sealed by means of gaskets to prevent dielectric fluid 32 such as oil surrounding the central conductor fro-m either leaking through the outer shell or through to the inside of the central conductor. The bushing is filled with the oil to a desired level, and oil may circulate through the entire bushing by means of holes 33 in the top cover plate.

A flange 34 welded to the metallic cylinder 14 provides means for mounting the bushing on the top electricai apparatus. As illustrated in Fig. l, the bushing is mounted on a circuit breaker 35, with the bottom of the central conductor 11 electrically contacting a circuit breaker contact assembly 36. Oil 37 in the circuit breaker tank 38 may enter the central conductor, but is prevented by the means previously described from contaminating the bushing oil.

The top of the bushing, when used with a circuit breaker, is illustrated in Fig. 2, wherein it is shown that current flowing through the central conductor 11 to the top terminal 25 passes through the braids 3(9, and the bellows 27. The braids are provided since the bellows cannot carry the full current.

Referring now to Fig. 3, the bushing is illustrated in use on a transformer. A central cable 40 is here provided to carry the current. The upper end of the cable 40 is provided with a threaded connector 41, the threaded connector being held in the central hole in the cover plate 24 by means of a pin 42. A top terminal 43 is threaded to the end of the connector 41.

From the following description it may be seen that there is no significant difference between the bushing structure of this invention whether used on transformers or on circuit breakers. slightly diiferent top terminal, an additional cable connector, and a pin. These differences are minor, however, and stocking of extra terminal parts if desired involves no difiiculty.

The bushing of this invention is therefore interchangeable between transformers and circuit breakers, and if one bushing breaks down or is damaged in use it may be replaced by bushings borrowed from either circuit breakers or transformers which are not in use at that time. Or if desired, one bushing may be kept in stock for replacement on either type of equipment.

It will be understood, of course, that, while the form of the invention herein shown and described constitutes a preferred embodiment of the invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications of the invention. It will be understood also, that the words used are words of description rather than of limitation, and that various changes, such as changes in shape, relative size, and arrangement of parts, may be substituted without departing from the spirit or scope of the invention herein disclosed.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrical insulating bushing for high voltage electrical apparatus of the type having a hollow central conductor surrounded at least in part by an insulating shell and having a dielectric fluid filled chamber between said conductor and said shell, an enclosed expansion chamber communicating with said dielectric fluid chamher and positioned axially on the top end of said bushing, said central conductor extending into said expansion chamber, an electric terminal rigidly positioned on said expansion chamber, metallic tubular means having an axially resilient portion and connecting the top of said conductor to said terminal internally to said expansion chamber for preventing the flow of fluids between said expansion chamber and the inside of said conductor and absorbing axial movement of said conductor with respect to said electric terminal, and flexible conductor means connected across the resilient portion of said tubular The transformer does use a ,4 means, said flexible conductor means and metallic tubular means being electrically connected to said central conductor and said terminal.

2. In an electrical bushing for high voltage electric apparatus of the type having a hollow central conductor surrounded at least in part by an insulating shell and having adielectric fluid filled chamber between said conductor and said shell, an enclosed expansion chamber communicating with said dielectric fluid chamber and positioned axially on the top end of said bushing, the top end of said central conductor extending through one side of said expansion chamber, an electric terminal rigidly positioned axially with respect to said central conductor and on the opposite side of said expansion chamber, metallic bellows means extending in said expansion chamber between said top end of said central conductor and said erminal, said bellows means preventing flow of fluids between said expansion chamber and the inside of said central conductor and absorbing axial movement of said conductor with respect to said terminal, and at least one flexible braid conductor connected externally across said bellows means, said braid conductor and bellows means being electrically connected to said central conductor and said terminal.

3. A high voltage insulating bushing for electrical apparatus comprising a hollow central conductor extending through a top and a bottom clamp plate means, said central conductor being radially surrounded by a shell extending between said top and bottom clamp means, said shell being comprised at least in part of insulating material and enclosing an annular dielectric fluid filled chamber surrounding said central conductor, a resilient connection between said central conductor and said top clamp plate means, metallic bellows means having one end sealed axially to the top end of said central conductor and the other end sealed to one end of a conducting sleeve, the other end of said sleeve being connected to a top terminal, flexible braid conductor means connected externally around the resilient portion of said bellows means, and an enclosed expansion chamber communicating with said fluid filled chamber and radially surrounding said bellows means between said top clamp plate means and said top terminal, said braid conductor means and bellows means being electrically connected to said central conductor and conducting sleeve.

4. A high voltage insulating bushing for electrical apparatus comprising a hollow central conductor extending through a top and bottom clamp plate means, a rigid connection between said central conductor and said bottom clamp plate means and a resilient connection between said central conductor and said top clamp plate means, said central conductor being surrounded by a shell extending between said clamp plate means and enclosing an annular dielectric fluid filled chamber surrounding said central conductor, said shell being comprised of a top insulating member, a central flange member, and a bottom insulating member, metallic bellows means having one end sealed axially to the top end of said central conductor and the other end sealed to one end of a conducting sleeve, the other end of said sleeve being connected to a top terminal, at least one flexible braid conductor connected externally around the resilient portion of said bellows means, an enclosed expansion chamber rigidly positioned between said top clamp plate means and said top terminal and radially surrounding said bellows means, and aperture means through said top clamp plate means providing communication between said fluid filled chamber and said expansion chamber, said bellows means and braid conductor being electrically connected to said central conductor and terminal.

5. A high voltage insulating bushing for interchangeable use on transformers and circuit breakers comprising a hollow central conductor extending rigidly through a bottom clamp plate and slidably through a top clamp plate, a shell radially surrounding said central conductor and enclosing an annular dielectric fluid filled chamber surrounding said central conductor, said shell comprising a top shell portion, a central flanged portion for mounting said bushing, and a bottom shell portion, compression spring means on the top end of said central conductor resiliently holding said top clamp against said top shell portion to allow for diflerent coefficients of expansion of said central conductor and said shell, an enclosed expansion chamber communicating with said dielectric fluid filled chamber and positioned axially with respect to said central conductor on the top side of said top clamp plate, said central conductor extending through one side of said expansion chamber, a top terminal extending through the opposite side of said expansion chamber, metallic bellows means extending in said expansion chamber connecting said top end of said central conductor to said terminal and preventing said dielectric fluid from entering the hole through said central conductor, and at least one flexible braid conductor in said expansion chamber connected across the resilient portion of said bellows means, said bellows means and braid conductor being electrically connected to said central conductor and terminal.

6. A high voltage insulating bushing for interchangeable use on transformers and circuit breakers comprising an inner conducting portion radially surrounded by an external dielectric fluid filled shell portion, said inner conducting portion comprising a hollow central conductor having a bottom end extending through the bottom of said bushing and a top end axially sealed to one end of a metallic bellows means, the other end of said bellows means being connected to one end of a conducting sleeve, the other end of said conducting sleeve being connected to a terminal, and at least one flexible braid conductor connected externally across the resilient portion of said bellows means, said inner conducting portion being adapted for passing a conducting cable therethrough from said bottom end of said central conductor to said terminal and being liquid tight except for the hole in said bottom end, said shell portion comprising a bottom clamp plate rigidly affixed to said bottom end of said central conductor, a top clamp plate slidably afiixed to the top end of said central conductor, a bottom insulating shell, central flanged shell, and top insulating shell compressed between said clamp plates, resilient means holding said top clamp plate against said top insulating shell, and an enclosed expansion chamber rigidly positioned between said top clamp plate and said terminal, said braid conductor and bellows means being electrically connected to said central conductor and said terminal.

7. In a high voltage electrical insulating bushing of the dielectric fluid filled type having a hollow central conductor surrounded at least in part by an insulating shell and extending into an expansion chamer, conducting means connecting the end of the said condutor in said chamber to terminal means mounted on said chamber,

said conducting means comprising first metallic tube means having one end sealed to said end of said conductor and the other end sealed to one end of a metallic bellows, second metallic tube means having one end sealed to said terminal means and the other end sealed to the other end of said bellows, and flexible braid conductor means connected between said tube means externally of said bellows, said first and second tube means being electrically connected to said central conductor and terminal means respectively, and to said bellows and braid conductor means.

8. In a high voltage electrical insulating bushing of dielectric fluid filled type having a hollow central conductor surrounded at least in part by an insulating shell and extending into one side of an expansion chamber, conducting means connecting the end of said conductor in said chamber to terminal means mounted on the opposite side of said chamber, said conducting means comprising first metallic tube means having one end sealed to said end of said conductor and the other end sealed to one end of a metallic bellows, second metallic tube means having one end sealed to said terminal means and the other end sealed to the other end of said bellows, and flexible braid conductor means connected between said tube means externally of said bellows, said tube means, bellows, and terminal extending axially of said conductor, said first and second tube means being electrically connected to said central conductor and terminal means respectively, and to said bellows and braid conductor means.

9. In a high voltage electrical insulating bushing of the dielectric fluid filled type having a hollow central conductor surrounded at least in part by an insulation shell and extending into one side of an expansion chamber, conducting means connecting the end of said conductor in said chamber to terminal means mounted over an aperture on the opposite side of said chamber, said conducting means comprising first tube means having one end threaded on and sealed to said end of said conductor, second tube means having one end flanged with the flange being held between said terminal means and the edges of said aperture, metallic bellows sealed between the other ends of said tube means, and flexible braid conductor means connected between said tube means externally of said bellows, said first and second tube means being electrically connected to said central conductor and terminal means respectively, and to said bellows and braid conductor means.

References Cited in the file of this patent UNITED STATES PATENTS 1,983,335 Austin Dec. 4, 1934 2,047,000 Calvert July 7, 1936 2,142,233 Brandt Jan. 3, 1939 2,623,919 Bowers Dec. 30, 1952 

